Our asthma research program involves both exposure assessment and prevention components, and focuses on the relationship between exposure to common indoor allergens and asthma prevalence and morbidity. The National Survey of Lead and Allergens in Housing (NSLAH), a study of allergen types and levels in floor and bedding dust in the nations housing, is the first study to provide estimates of allergen exposure in the U.S. population. It encompasses 831 homes in 75 primary sampling units located throughout the country. The major endpoints are measurements of dust mite, cockroach, cat, dog, mouse, rat and fungal allergen levels, and endotoxin in dust samples collected from an array of sites in the surveyed homes. Results from analysis of mouse allergens indicate that 82% of U.S. homes have detectable levels of mouse allergen with 35% of homes having levels >1.6 microgram mouse allergen/gram dust a level associated with increased mouse allergen sensitization rates. In allergic individuals who also have active asthma, defined as having doctor-diagnosed asthma and asthma symptoms in the preceding 12 months, being exposed to levels of mouse allergen >1.6 microgram mouse allergen/gram dust increased the odds of having asthma symptoms. Asthmatic individuals, who did not report having allergies, did not have increased odds of having symptoms when exposed to elevated mouse allergen levels in their homes. Household exposure to endotoxin has emerged as an important factor in the development and severity of asthma in those who do not have allergies. We previously reported from NSLAH that increasing concentration of endotoxin in homes was a risk factor for increased prevalence of diagnosed asthma, asthma symptoms in the past year, current use of asthma medications, and wheezing. Because of the importance of limiting endotoxin exposures, particularly among asthmatic individuals, several studies have evaluated the predictors of endotoxin concentration in house dust or endotoxin loading of surfaces in homes. In general, these studies have been confined to a particular geographic area, demographic group, or type of housing;and most have been limited to either the family room floor dust or bedding. Because of the targeted scope of these studies and the focus on one or two municipalities, some contradictory findings have emerged, raising the question as to the generalizability of the findings. The NSLAH provided the opportunity to investigate the predictors of endotoxin contamination in housing in a nationwide sample designed to represent the U.S. population. Weighted geometric mean endotoxin concentration ranged from 18.7 to 80.5 endotoxin units (EU)/mg for the five sampling locations, and endotoxin load ranged from 4,160 to 19,500 EU/m2. Increased endotoxin in household reservoir dust is principally associated with poverty, people, pets, household cleanliness, and geography. We have also worked with investigators at the CDC/NCHS to implement the allergen and asthma component of NHANES 2005-2006. We collected bedroom dust, measured total and allergen-specific IgE and assessed asthma and allergy prevalence and morbidity in approximately 9000 individuals in the U.S. Analysis of this large dataset will allow us to 1) estimate nationwide prevalence of indoor allergen and endotoxin exposures, 2) estimate nationwide prevalence of allergic sensitization to indoor, outdoor and food allergens, 3) estimate nationwide prevalence of allergic diseases including asthma, and 4) investigate the complex relationships between allergen and endotoxin exposures, allergic sensitization and allergic diseases including asthma. In analysis of IgE levels to estimate nationwide prevalence of allergic sensitization, median total IgE values were found to be higher for males than for females;for non-Hispanic Blacks and Mexican-Americans than for non-Hispanic whites;for those with less than a 12th grade education, increased poverty, higher serum cotinine levels, and higher body mass indices;and for those with at least 1 positive specific IgE result. Current asthma was reported by 8.8% of the population. The prevalence of asthma differed significantly by age, race/ethnicity, sex, poverty, serum cotinine level, and body size. The prevalence of asthma was higher among allergic than non-allergic individuals. The geometric mean for total IgE level was significantly higher among asthmatics than non-asthmatics. Among the US population 6 years and older, total serum IgE levels were associated with doctor-diagnosed current asthma but only among persons who had allergies.